Hubba hubba! Now you're talking my old "stompin' grounds." My parents still have their cottage in Wareham, just off of Great Neck Road.
(well, summer grounds, since we lived about 45 minutes north)
Granted it's been a while since I've been there, so the couple places I come up with may or may not be there.
Onset/Onset Harbor is an all around fun place to spend some time. Beautiful property with a great view of the harbor. They used to have a touristy boat called the "Viking" that went through the harbor and down the Canal some. When I was a kid (maybe I should say when I was younger) the captain let me drive the Viking, with a boatload of passengers! I thought that was so cool!
Anyways, there are a few little shops in the 'hood as well. For restaurants, Marc Anthony's is a corner pizzaria right close to the Viking dock (just west) that makes a pretty good pie. They aren't (or weren't at the time) a "chain" of any size, which I like. Then, just a few doors down to the west is (was) an ice cream place, I think it was called Grandma's. It had ice cream and candy as I recall. Good ice cream that didn't taste mass produced (not that massed produced is bad, but you know what I mean). Diagonally NE of Marc Anthony's is (was) a place that was a up scale restaurant, I think called The Lighthouse, but I am not sure. Like I said, a more classy type restaurant, at least at the time.
The other family favorite is Sandy's. They have two locations, one just on the mainland side of the Bourne Bridge, and one in Sandwich. The one in Sandwich has a bit more of a classy casual atmosphere, while the one is Bourne is straight up family atmosphere. The food is fantastic, and plenty of it. For the "adult" entrees, they have a children's portion size, and an adult portion size (they do have a kids menu besides). We pretty much always got the children's portion size because the quantity of food. With increased costs though, the quantity may be different. I remember Dad got the Fisherman's Platter, full size, that could have fed he, Mom, and me with the one plate!
Getting to Sandy's in Bourne may be tricky, cause of the rotary. You actually take a side road that appears to lead to a hotel and a Salvation Army Thrift store to get there.
Also on this rotary is (was) the Tug Boat, which serves ice cream. Good stuff there, a lot like the place in Onset but more flavors and a cooler atmosphere.
Right next to the Tug Boat is (was) Grandma's Something or other (Pie was in the title somewhere) and Grampy's Tavern right next door. I don't recall eating there, but it always looked really good.
You've likely planned out activities, but here are a couple cool things I recall (outside of Onset).
1. The MA Maritine (sp?) Academy in Buzzards Bay. This is right at the western entrance to the Canal, by the railroad lift bridge (which also has an entrance to get to the bike/walking path on the Canal). A great place to see the MMA ship if docked, but to also see the ships and boats going through the Canal. Always some fishermen there too that have a tale or two to tell.
2. The Christmas Tree Shop was a must stop for my family. It's on the Cape side of the Sagamore Bridge, SE corner. Great stuff at unbelievably low prices, open year round. Also, on the SW corner is a huge outlet mall that is certainly worth checking out. Between these two locations, you may need a second, or at least larger, vehicle!
3. Cape Cod Potato Chip factory is in Hyannis, real close to the Hyannis Mall. I recall it being an interesting tour with a free bag of CC Potato Chips for everyone at the end. Also, the Food Court at the Hyannis Mall is huge!
4. Back in Wareham, if I recall correctly, they have a semi-pro baseball team that plays on the west side of town, on the way to Marion and Mattepoisett (sp?).
Also, if there are any golfers in the family, Little Harbor Country Club is a great course, and where I learned to play, right in Wareham. It's a nice 18 hole course next to Little Harbor Beach. You needed a pass to get to the beach, but day passes were available, so while some golf, others could be at the beach. It's a huge, beautiful beach.
Back to food, the trusty usuals are available, including Papa Gino's and Freindly's (a personal favorite of mine) right close.
As you likely know, there is a lot to do down at the Cape. Go further south to get to the National Oceanic something or other, which is where the ferries to get to Martha's Vineyard (and Nantucket Island, I think) are. Go out to the tip of the Cape to Provincetown to see some cool scenery.
I'm sure I've missed some, likely a lot, but these are what I recall as highlights of my ventures down on the Cape.